Process for optimizing a core die

ABSTRACT

A process for optimizing a core die is provided. By iteratively modifying the ceramic core without changing the core die, it is possible to ascertain an optimum core without modifying the core die every time. In a last step, an optimum core die is produced using the optimum ceramic core.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European Patent Office application No. 10189844.3 EP filed Nov. 3, 2010, which is incorporated by reference herein in its entirety.

FIELD OF INVENTION

The invention relates to a process for optimizing a core die.

BACKGROUND OF INVENTION

Core dies are used to produce ceramic cores for casting metallic cast components in ceramic casting molds.

After the ceramic core has been used for the casting, it is sometimes established that certain deviations arise in the interior of the cast component, and therefore the core die has to be modified.

This is the case, for example, in turbine blades or vanes which are hollow on the inside and in which the inner hollow space has a cooling structure. In this case, a cooling medium also flows out of the turbine blade or vane. Deviations in the core die and therefore in the ceramic core can lead to an increased consumption of cooling air, and this is not desired.

It is expensive to solve the problem of a deviation using a new, varied core die, however, particularly if it is necessary to run through a plurality of iterations.

SUMMARY OF INVENTION

It is therefore an object of the invention to specify a process for simplifying this problem which is less expensive to carry out.

The object is achieved by a process as claimed in the claims.

The dependent claims list further advantageous measures which can be combined with one another, as desired, in order to achieve further advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 show the schematic sequence of the process,

FIG. 6 shows a ceramic core with additional elevations or depressions,

FIG. 7 shows a turbine blade or vane,

FIG. 8 shows a gas turbine, and

FIG. 9 shows a list of superalloys.

The descriptions of the figures represent only exemplary embodiments of the invention.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a ceramic core 10′ which has been produced using a core die 1′.

The core die 1′ has, in particular, two shells or half-shells 3′, 7′.

After the first casting (FIG. 2) using such a ceramic core 10′, it may be established, for example, that deviations are present, and that the flow of coolant (flow rate) through the interior 25′ of the cast component 13′ deviates, i.e. is too high or too low.

However, the core 10′ is once again produced using the core die 1′, 3′, 7′ which produced improper cores 10′. The ceramic core 10′ is then provided with a modification 16 (FIG. 3), in particular uniformly, very particularly with elevations 19 (FIG. 6), in particular if the flow rate is too high.

The elevations 19 (FIG. 6) can be applied at various points along a radial or other direction, uniformly or only in a partial region 22 (FIG. 6) of the core 10′.

Using the thus modified core 10″, a casting process is again carried out and it is again checked whether the cast component 13″ complies with the specification for flow rate measurement (FIG. 4). If this is the case, the core die 1′ can be modified by means of the result of the modified ceramic core 10″ with the elevations 16, 19, it then being ensured that this core die 1″ also supplies cores which comply with a desired specification (FIG. 5).

If, furthermore, deviations are established, the next modification of the core 10′, 10″ takes place with less/more higher or wider elevations or other modifications on the core 10′, 10″.

The elevations 19 or modifications 16 on the ceramic core 10′ can be produced more quickly and more favorably, without having to completely modify the expensive core die 1′ in one or more iterations.

Using an optimized core 10″, it is possible to produce a new core die 1″ which can then be used for series production (FIG. 5).

FIG. 7 shows a perspective view of a rotor blade 120 or guide vane 130 of a turbomachine, which extends along a longitudinal axis 121.

The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor.

The blade or vane 120, 130 has, in succession along the longitudinal axis 121, a securing region 400, an adjoining blade or vane platform 403 and a main blade or vane part 406 and a blade or vane tip 415.

As a guide vane 130, the vane 130 may have a further platform (not shown) at its vane tip 415.

A blade or vane root 183, which is used to secure the rotor blades 120, 130 to a shaft or a disk (not shown), is formed in the securing region 400.

The blade or vane root 183 is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible.

The blade or vane 120, 130 has a leading edge 409 and a trailing edge 412 for a medium which flows past the main blade or vane part 406.

In the case of conventional blades or vanes 120, 130, by way of example solid metallic materials, in particular superalloys, are used in all regions 400, 403, 406 of the blade or vane 120, 130.

Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949.

The blade or vane 120, 130 may in this case be produced by a casting process, by means of directional solidification, by a forging process, by a milling process or combinations thereof.

Workpieces with a single-crystal structure or structures are used as components for machines which, in operation, are exposed to high mechanical, thermal and/or chemical stresses.

Single-crystal workpieces of this type are produced, for example, by directional solidification from the melt. This involves casting processes in which the liquid metallic alloy solidifies to form the single-crystal structure, i.e. the single-crystal workpiece, or solidifies directionally.

In this case, dendritic crystals are oriented along the direction of heat flow and form either a columnar crystalline grain structure (i.e. grains which run over the entire length of the workpiece and are referred to here, in accordance with the language customarily used, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of one single crystal. In these processes, a transition to globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably forms transverse and longitudinal grain boundaries, which negate the favorable properties of the directionally solidified or single-crystal component.

Where the text refers in general terms to directionally solidified microstructures, this is to be understood as meaning both single crystals, which do not have any grain boundaries or at most have small-angle grain boundaries, and columnar crystal structures, which do have grain boundaries running in the longitudinal direction but do not have any transverse grain boundaries. This second form of crystalline structures is also described as directionally solidified microstructures (directionally solidified structures).

Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1.

The blades or vanes 120, 130 may likewise have coatings protecting against corrosion or oxidation e.g. (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (Hf)). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1.

The density is preferably 95% of the theoretical density.

A protective aluminum oxide layer (TGO=thermally grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer).

The layer preferably has a composition Co-30Ni-28Cr-8Al-0.6Y-0.7Si or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective coatings, it is also preferable to use nickel-based protective layers, such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re.

It is also possible for a thermal barrier coating, which is preferably the outermost layer and consists for example of ZrO₂, Y₂O₃—ZrO₂, i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX.

The thermal barrier coating covers the entire MCrAlX layer.

Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD).

Other coating processes are possible, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include grains that are porous or have micro-cracks or macro-cracks, in order to improve the resistance to thermal shocks. The thermal barrier coating is therefore preferably more porous than the MCrAlX layer.

Refurbishment means that after they have been used, protective layers may have to be removed from components 120, 130 (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the component 120, 130 are also repaired. This is followed by recoating of the component 120, 130, after which the component 120, 130 can be reused.

The blade or vane 120, 130 may be hollow or solid in form. If the blade or vane 120, 130 is to be cooled, it is hollow and may also have film-cooling holes 418 (indicated by dashed lines).

FIG. 8 shows, by way of example, a partial longitudinal section through a gas turbine 100.

In the interior, the gas turbine 100 has a rotor 103 with a shaft 101 which is mounted such that it can rotate about an axis of rotation 102 and is also referred to as the turbine rotor.

An intake housing 104, a compressor 105, a, for example, toroidal combustion chamber 110, in particular an annular combustion chamber, with a plurality of coaxially arranged burners 107, a turbine 108 and the exhaust-gas housing 109 follow one another along the rotor 103.

The annular combustion chamber 110 is in communication with a, for example, annular hot-gas passage 111, where, by way of example, four successive turbine stages 112 form the turbine 108.

Each turbine stage 112 is formed, for example, from two blade or vane rings. As seen in the direction of flow of a working medium 113, in the hot-gas passage 111 a row of guide vanes 115 is followed by a row 125 formed from rotor blades 120.

The guide vanes 130 are secured to an inner housing 138 of a stator 143, whereas the rotor blades 120 of a row 125 are fitted to the rotor 103 for example by means of a turbine disk 133.

A generator (not shown) is coupled to the rotor 103.

While the gas turbine 100 is operating, the compressor 105 sucks in air 135 through the intake housing 104 and compresses it. The compressed air provided at the turbine-side end of the compressor 105 is passed to the burners 107, where it is mixed with a fuel. The mix is then burnt in the combustion chamber 110, forming the working medium 113. From there, the working medium 113 flows along the hot-gas passage 111 past the guide vanes 130 and the rotor blades 120. The working medium 113 is expanded at the rotor blades 120, transferring its momentum, so that the rotor blades 120 drive the rotor 103 and the latter in turn drives the generator coupled to it.

While the gas turbine 100 is operating, the components which are exposed to the hot working medium 113 are subject to thermal stresses. The guide vanes 130 and rotor blades 120 of the first turbine stage 112, as seen in the direction of flow of the working medium 113, together with the heat shield elements which line the annular combustion chamber 110, are subject to the highest thermal stresses.

To be able to withstand the temperatures which prevail there, they may be cooled by means of a coolant.

Substrates of the components may likewise have a directional structure, i.e. they are in single-crystal form (SX structure) or have only longitudinally oriented grains (DS structure).

By way of example, iron-based, nickel-based or cobalt-based superalloys are used as material for the components, in particular for the turbine blade or vane 120, 130 and components of the combustion chamber 110.

Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949.

The blades or vanes 120, 130 may likewise have coatings protecting against corrosion (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon, scandium (Sc) and/or at least one rare earth element, or hafnium). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1.

It is also possible for a thermal barrier coating to be present on the MCrAlX, consisting for example of ZrO₂, Y₂O₃—ZrO₂, i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide.

Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD).

The guide vane 130 has a guide vane root (not shown here), which faces the inner housing 138 of the turbine 108, and a guide vane head which is at the opposite end from the guide vane root. The guide vane head faces the rotor 103 and is fixed to a securing ring 140 of the stator 143. 

1-4. (canceled)
 5. A process for producing a new core die for a ceramic casting core, comprising: producing a ceramic core using an initial core die; carrying out a casting process using the ceramic core, and carrying out specification measurements on an obtained cast component, wherein when the cast component deviates from its desired values, the initial core die is not modified, but instead the ceramic core is in turn produced using the same initial core die and the ceramic core is processed to form a modified core, wherein the modified core is used for casting until the modification of the ceramic core or the modified core have the effect that the cast component complies with the required specifications, and wherein the new core die is then produced using the modified core.
 6. The process as claimed in claim 5, wherein elevations are produced as the modification or are modified.
 7. The process as claimed in claim 5, wherein the modification is distributed only in a partial region of the modified core.
 8. The process as claimed in claim 5, wherein a rate of flow through an interior of the cast component is determined in order to determine a deviation from the specification. 